The most common model of laser cutting machine for flat sheet metals is that having moving optics and a fixed piece. In such a machine model, the sheet being processed is arranged on a plane while the cutting tool (focusing head) is moving along movement axes X-Y perpendicular to each other and parallel to the plane of the sheet, by means of suitable CNC actuators. Generally, the first axis (X) is that with the longest stroke and is made with a gantry resting on two parallel guides or on a single guide with a cantilever. The second orthogonal axis (Y) is generally mounted to the first. The total mass of the moving equipments along the two axes thus conceived is generally rather significant, despite being in line with the task.
The flat laser cutting profiles generally comprise a multitude of small winding movements which, to be travelled with sufficient accuracy, require the adoption of limited dynamics which are reflected in a lower machine productivity. The dynamics (maximum accelerations) are limited due to the masses involved. The structure having a central beam, used as a middle way between the gantry and cantilever solutions, is also affected by this problem. In other words, the masses of the system of Cartesian axes X-Y and the accelerations required to cut contours with small curvature radiuses at the processing speed, are against the current trend. We point out that the acceleration while bending is v2/r, where “v” is the specific laser cutting processing speed and “r” is the curvature radius of the cutting profile in progress. If “r” is small, then the acceleration becomes high and the processing speed “v” should be reduced to obtain a quality processing.
A first solution adapted to overcome the afore-described limit was achieved by adding a second system of auxiliary Cartesian axes xy, with reduced masses and strokes, mounted on the first system of main axes XY (patent US 2004/0025761). In a work cycle; a few long-pitch movements are made with the main axes XY and many local movements having a short pitch and high dynamics are made with the pair of auxiliary Cartesian axes xy (solution XY+xy).
An alternative solution was then devised and described in EP1366846 using a single additional, linear auxiliary axis x mounted on the transversal axis Y, in turn upheld by the main gantry X. The dominating mass is that of the main gantry X while the small mass is given by the transversal axis Y and the auxiliary x. The wide, rare movements are performed with the axis of the main gantry X while the local, frequent movements having high dynamics are performed with the pair of axes Yx (X+Yx solution).
A further alternative solution came out with US 2008/0197118, which substitutes the additional Cartesian system xy at low inertia with a polar positioning mechanism “ρΘ” operated by two motorized slides of adjustable length which extend towards the cutting head from a common motorized carriage which is slidable along the axis Y. The wide, rare movements are performed with the gantry axis X while the local, frequent movements having high dynamics are performed with the combination of the three axes YρΘ (X+Yρ{tilde over (Θ)} solution).